Hearing aid

ABSTRACT

A control voltage is produced by rectifying lower and higher frequency portions of an output from a microphone and applied to a low-band and a high-band control circuit to decrease the lower and higher frequency of the output from the same microphone or a separate microphone to adjust the frequency characteristic in accordance with the auditory characteristic of a person having difficulty in hearing.

Nakamura et a1.

[ Dec. 16, 1975 HEARING AID [56] References Cited [75] Inventors: Kenji Nakamura, Chigasaki; UNITED STATES PATENTS Fukuyama; TakuO 2,112,569 3/1938 Lybarger 179/107 FD Yamamom, both of Tokyo, 3110f 3,385,937 5/1968 Lafon 179/107 R Japan 3,764,745 lO/1973 Bottcher 179/107 FD Assignee2 Rio Kabushiki Kaisha, Kokubunji, 3,784,750 I/ 1974 Stearns 179/107 FD .Ia an p Primary Examiner-Ralph D. Blakeslee Flledi p 1973 Attorney, Agent, or FirmWenderoth, Lind & Ponack [21] Appl. No.: 354,145 1 [44] Published under the Trial Voluntary Protest [57] ABSTRACT Program on January 1975 as document A control voltage is produced by rectifying lower and B 354,145 higher frequency portions of an output from a microphone and applied to a low-band and a high-band cong Application Priority Data trol circuit to decrease the lower and higher frequency 001. 16, 1972 Japan 47403466 of the output from th sa mi r phone r a separat microphone to adjust the frequency characteristic in [52] US. Cl. 179/107 FD c or n i h the a i ory charac eris i of a p r- [51] Int. Cl. H04R 25/00 n ng e lty in h r ng. [58] Field of Search 179/107 R, 107 FD I 8 Claims, 10 Drawing Figures .1 L 1 i 2 )6 i 8 2 M y o 'CROPHONE EARPHONE US. Patent Dec. 16, 1975 Sheet20f3 3,927,279

FIG.

m U Z .5950

FREQUENCY IN KHz FREQUENCY IN KHz mu Z .SnFDO FIG.

VC=CONTROL VOLTAGE mu Z P3950 FREQUENCY IN KHZ HEARING AID BACKGROUND OF THE INVENTION This invention relates to improvements in hearing aid devices and more particularly to hearing aid devices through which persons having difficulty in hearing can obtain more intelligence under more comfortable conditions than those otherwise obtainable.

A great number of persons having difficulty in hearing have auditory characteristics presenting recruitment in the higher frequency band of the acoustic spectrum. When using hearing aids, those persons are frequently subject to pain caused by loud sounds in the higher frequency band. Also where the persons use hearing aids to make conversations in noisy areas, for example, in a city, they have experienced, in addition to the problem of the pain as above described, the obstruction of conversations with those frequencies of the acoustic spectrum not required for the conversation becuase the noise is of a broad frequency band. While conventional hearing aids have included means for adjusting their frequency characteristic in accordance with the auditory characteristics of the particular user, there has been previously proposed no means to eliminate obstacles under acoustic circumstances such as above described.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a new and improved hearing aid device capable of imparting more intelligence to the hard of hearing user than otherwise obtainable.

The present invention accomplishes this object by the provision of a hearing aid device comprising, in combination, at least one microphone for picking up acoustic energy to convert it to a corresponding electrical energy, a control generator circuit for generating a control voltage in response to that portion of the converted electrical energy having a predetermined frequency spectrum, and control circuit means responsive to the control voltage from the control generator circuit to control the frequency characteristic of the electrical energy.

The control generator circuit may preferably generate the control voltage by rectifying that portion of the electrical energy corresponding to those frequency portions of the acoustic spectrum not required for conversations.

The control generator circuit may conveniently include a band-rejection filter for rejecting those frequency portions of the electrical energy corresponding to thosefrequency portions of the acoustic spectrum required for conversations.

The control circuit means may advantageously include a lower-band control circuit responsive to the control voltage from the control generator circuit to control the lower frequency portions of the electrical energy, and a higher-band control circuit responsive to the control voltage from the control generator circuit to control the higher frequency portions of the electrical energy.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will become more readily apparent from the following detailed description .taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram of a hearing aid device constructed in accordance with the principles of the prior art;

FIG. 2 is a combined block and circuit diagram of a hearing aid device constructed in accordance with the principles of the present invention;

FIG. 2a, is a wiring diagram showing a circuit equivalent to the control circuit for controlling the lower frequency band as shown in FIG. 2;

FIG. 2b and 2c are wiring diagrams of circuits equivalent to the control circuit for controlling the higher frequency band as shown in FIG. 2;

FIG. 3 is a schematic circuit diagram of the lowerband control circuit shown in FIG. 2 and a graph illustrating the frequency characterisitc thereof dependent upon a control voltage applied thereto;

FIG. 4 is a schematic circuit diagram of the higherband control circuit shown in FIG. 2 and a graph illustrating the frequency characteristic thereof dependent upon a control voltage applied thereto;

FIG. 5 is a block diagram of amodification of the present invention;

FIG. 5a is a wiring diagram of a circuit equivalent to the lower-band control circuit as shown in FIG. 5; and

FIG. 6 is a graph illustrating the overall frequency characteristic provided by the present invention with the parameter being a control voltage applied thereto.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 of the drawings, there is illustrated a conventional hearing aid device. In the arrangement illustrated a microphone. 10 picks up an acoustic energy to convert it to a corresponding electrical energy or signal which is, in turn, amplified by an amplifier 12 connected to the microphone 10. The amplified signal is applied through one arm of a transfer switch SW to a selected one of a plurality, of filters, in this case three, 14a, 14b and shown as being a highpass, a low-pass and a band-pass filter respectively. Then an output from the selected filter 14 is given a frequency characteristic most adapted to the auditory characteristic of the particular hard of hearing user after which it is supplied through the other arm of the transfer switch SW to a volume control 16. The volume control 16 is set to control an output therefrom to a suitable amplification degree. The output from the volume control 16 is amplified by the succeeding amplifier l8 and thence to an earphone 20 through which the user can listen an audio sound corresponding to the acoustic energy picked up by the microphone 10. The arrangement could have generally added thereto a circuit for limiting an output therefrom (not shown).

Therefore the arrangement as shown in FIG. 1 has the important feature of adjusting the frequency characteristic thereof in accordance with the auditory characteristic of the user. However, this feature alone cannot solve the problems of preventing the user from being painfully subject to loud sounds having the higher frequencies and causing a conversation made in noisy regions to be obstructed by sound not required for the conversation.

The present invention contemplates to solve those problems.

Referring now to FIG. 2, there is illustrated a hearing aid device constructed in accordance with the princi' ples of the present invention. The arrangement illustrated includes a control generator circuit generally designated by the reference numeral 22 and comprising a control microphone 24 for picking up acoustic energy to convert it to a corresponding electrical energy or signal, an amplifier 26 connected to the microphone, and a band-rejection filter 28 to reject those frequency portions of the electrical signal corresponding to those frequency portions of the acoustic spectrum required for conversations but to permit those frequency portions of the acoustic spectrum not required for conversations to pass therethrough. Those frequencies required for conversations of the acoustic spectrum may range from about 300 hertz to about 3,000 hertzs. Then the filter 28 is connected to a semi-fixed volume control 30 subsequently connected through an amplifier 32 to a rectifier circuit 34.

The arrangement further includes a conversation microphone 36 for picking up acoustic energy to convert it to a corresponding electrical energy or signal for the purpose of transmitting the converted electrical signal. to the associated earphone. The microphone 36 is preferably of a capacitance type and may be piezoelectric, a capacitor or an electroret microphone. The microphone 36 is connected to a lower-band control circuit generally designated by the reference numeral 38 and thence to a higher-band control circuit generally designated by the reference numeral 40. The control circuit 40 is capacitively coupled to an amplifier 42 connected to a volume control 44 subsequently connected to a separate amplifier 46. Then the amplifier 40 is connected to an earphone 48.

In operation, the band-rejection filter 28 is operated to cause those frequency portions of the amplified output voltage from the control microphone 24 not required for conversations to pass therethrough and to prevent the remaining frequency portions thereof from passing therethrough. The output from the filter 28 is controlled to a predetermined level by the volume control 30 and after amplification it is rectified into a positive control voltage by the rectifier circuit 34. The volume control 30 serves to set a control threshold level at which the control voltage is initiated to perform the control operation as will be described hereinafter.

The positive control voltage from the rectifier circuit 34 is applied to both control circuits 38 and 40. The control circuit 38 controls a lower frequency band, this is, lower frequency portions of an output voltage from the microphone 36 While the control circuit 40 controls a higher frequency band, that is, the higher frequency portions of the output voltage.

The lower-band control circuit 38 is shown in FIG. 2 as including an'NPN type transistor Q connected to both a semiconductor diode D and a field effect transistor Q and particularly suitable for use with the capacitive type of microphones which are extremely high in output impedance. Examples of such microphones include the capacitor or piezoelectric microphone as above described. More specifically, the transistor Q is preferably formed of semiconductive silicon and includes a base electrode connected to the output of the rectifier circuit 34, and a collector electrode connected to a source of voltage E and also to the drain electrode of the field effect transistor Q The transistor Q includes a source electrode connected to ground through a source resistor R, and a gate electrode connected to the junction of the emitter electrode of the diode Q and the cathode electrode of the diode D The diode D is prefi'ably formed of a semiconductive silicon and connected across the microphone 36 with the anode electrode thereof connected to ground. The diode D serves as a load for the microphone 36 and also presents a leakage impedance to the gate electrode of the field effect transistor Q through the utilization of a high impedance presented thereby at about a null voltage. If desired, the diode D may be replaced by a high resistance.

The silicon transistor Q has the emitter and collector electrodes connected to the gate and drain electrodes of the field effect transistor Q respectively, and the base electrode having applied thereto a positive control voltage supplied from the rectifier circuit 34. Under these circumstances the positive control voltage equal to or less than about 0.6 volt with respect to a voltage at the emitter electrode of the transistor Q causes an impedance between the emitter and collector electrodes thereof to be very high. If the positive control voltage exceeds the figure just described then the impedance is begins to decrease.

The lower-band control circuit 38 has an equivalent circuit as shown in FIG. 2a. In FIG. 2a, a series combination of a capacitance C, and a source E of alternating current representing the microphone 36 is connected across a parallel combination of a resistor D and a resistor Q corresponding to the components D and Q shown in FIG. 2. As above described, the transistor Q shown in FIG. 2 has an impedance variable with the control voltage applied to the base electrode thereof and the resistor Q is shown in FIG. 2a as being variable. Therefore the control circuit 38 forms a C-R filter for differently controlling the lower frequency portions of the electrical signal in'accordance with the positive value of the control voltage.

The electrical signal thuscontrolled is developed across the source resistor R of the field effect transistor Q and supplied to the higher-band control circuit 40 through a capacitor C The control circuit 40 includes a C-R type high pass filter connected to the coupling capacitor C and having series resistors R and R and parallel capacitors C and C interconnected in the manner as shown in FIG. 2, and an NPN type transistor Q having a base electrode connected to the C-R filter, a collector electrode connected to the output of the rectifier circuit 34 and an emitter electrode connected to ground through an emitter resistor R The circuit 40 forms a negative feed back amplifier well known in the art as seen in FIG. 2b wherein an equivalent circuit thereof is illustrated.

In the higher-band control circuit 40, the control voltage applied from the rectifier circuit 34 to the collector electrode of the transistor Q can change to vary a current gain B thereof to change an amplification degree A of an amplifier formed of the transistor Q, be tween one and zero. A decrease in the amplification degree A causes a decrease in amplitude of the electrical signal in the higher frequency band. FIG. 20 shows a circuit equivalent to the control circuit 40 having its amplification degree A equal to a zero.

To demonstrate the manner in which the lower-band control circuit 38 controls the lower frequency portions of the electrical signal, the circuit 38 was formed, by way of example, of circuit parameters having values shown in FIG. 3. The microphone 36 had an effective capacitance of picofarads and the diode D had an equivalent impedance of 20 megohms while the transistor Q available as 2SC77 from Tokyo Shibaura Electric Co., had a collector potential maintained at 1.3 volts and a base potential successively changed to its values of 0.5, 0.6 and 0.7 volt in increments of 0.1 volt. The transistor Q was 2SK30 marketed by the Tokyo Shibaura Electric Co. Under these circumstances, a voltage across the resistor R of 5.6 kiloohms was plotted against a frequency as shown in FIG. 3 wherein the ordinate represents the output voltage in dBs and the abscissa represents the frequency in kilohertz with the parameter being the base potential of the transistor Q. As shown in FIG. 3, the lower frequency portion of the electrical signal decreases as the base potential or control voltage increases.

FIG. 4, similar to FIG. 3, illustrates the higher-band control circuit 40. From FIG. 4 it is seen that with the circuit 40 including its circuit parameters having values denoted in FIG. 4, the output voltage therefrom remains constant with respect to the frequency for the base potential of the transistor Q identical to the transistor Q for a control voltage of up to 0.4 volt. However, as the control voltagegradually increases from 0.4 to 0.9 volt in increments of 0.1 volt, the higher frequency portion of the electrical energy progressively decreases.

Thus it will be appreciated that both control circuits 38 and 40 are operated under the control of the positive control voltage to properly decrease the lower and higher frequency portions of the output voltage from the microphone 36 respectively. In other words, a voltage developed across the emitter resistor R is composed of an electrical signal corresponding to that acoustic signal required for conversations.

The voltage across the resistor R is then applied through a capacitor C to the amplifier 42 and thence to the earphone 48 through the volume control 44 and the amplifier 46. Therefore the user can listen only the acoustic signal required for conversation from the earphone 48 even in the case the user is positioned in acoustic circumstances including sounds not required for the particular conversation.

FIG. 5 wherein like reference numerals designate components identical or similar to those shown in FIG. 2, discloses an alternative embodiment of the subject invention. The arrangement illustrated is mainly different from that shown in FIG. 3 in the use of single microphone 36. More specifically, the microphone 36' functions as both the control microphone 24 and the conversation microphone 36 and is connected to the amplifier 22 and also to the lower-band control circuit 38 in a somewhat different manner from the circuit 38 as shown in FIG. 2. The lower band control circuit 38 includes a field effect transistor 0., having a gate electrode connected to a rectifier circuit 35 connected to the amplifier 32 to provide a negative control voltage. The transistor Q includes drain and source electrodes having a capacitor C connected thereacross and also the microphone 36 connected thereacross through a source resistor R The circuit 38 is equivalent to a circuit shown in FIG. 5a. The rectifier circuit 34 provides a positive control voltage to the higher band control circuit 40. In other respects, the arrangement is identical to that shown in FIG. 2.

FIG. 6 is a graph illustrating the overall frequency characteristic of an embodiment of the present invention with the control voltage changed from 0.5 to 0.9 volt in increments of 0.1 volt. FIG. 6 clearly illustrates the manner in which the lower and higher frequency portions of the frequency characteristic change with the control voltage.

While the present invention has been illustrated and described in conjunction with a few preferred embodiments thereof it is to be understood that numerous changes and modifications may be resorted to without departing from the spirit and scope of the invention. For example, the response of the control voltage to the output from the microphone 24 dependent upon the setting on the volume control 30 may gradually change from its dull to its sharp state by continuously varying the amplifier 32 from class A operation to class C operation. The term dull state means the response of the control voltage slowly changing with the output from the microphone 24 while the term sharp state means the response of the control voltage rapidly changing with the output from the microphone 24 above a certain level thereof. If desired, a plurality of filters, as shown in FIG. 1, may be properly connected in the arrangement such as shown in FIG. 3 or 5 in order to adapt the frequency characteristic of the arrangement to the auditory characteristic of the particular user having difficulty in hearing. Further suitable transfer switch means may be operatively coupled to either or both of the lower and higher band control circuits 38 and 40 in order to selectively put the latter in the fixed and semi-fixed modes of operation and the inoperative state.

What we claim is:

1. A hearing aid device comprising in combination, a pair of microphones each picking up acoustic energy to convert it to a corresponding electrical energy, a control generator circuit connected to one of the microphones to generate a control voltage in response to that portion of the electric energy generated by said one microphone having a predetermined frequency spectrum, a first control circuit connected to both the other microphone and to the control generator circuit to decrease the lower frequency portions of the electrical energy from the other microphone in response to the control voltage from the control generator circuit, and a second control circuit connected to the first control circuit and also to the control generator circuit to decrease the higher frequency portion of the electrical energy from the other microphone in response to the control voltage from the control generator circuit, whereby acoustic energy reconverted from the electrical energy has a frequency characteristic suitable for the auditory characteristic of a person having difficulty in hearing.

2. A hearing aid device as claimed in claim 1, wherein the control generator circuit includes rectifier means for rectifying that portion of the electrical energy corresponding to those frequency portions of the acoustic spectrum not required for conversations to generate the control voltage.

3. A hearing aid device as claimed in claim 1, wherein the control generator circuit includes a bandrejection filter for rejecting that frequency portion of the electrical energy corresponding to that frequency portion of the acoustic spectrum required for conversations.

4. A hearing aid device as claimed in claim 1, wherein the control circuit means includes a lowerband control circuit responsive to the control voltage from the control generator circuit to control the lower frequency portions of the electrical energy, and a higher-band control circuit responsive to the control voltage from the control generator circuit to control the higher frequency portions of the electrical energy.

5. A hearing aid device comprising in combination, a single microphone for picking up acoustic energy to convert it to a corresponding electric energy, a control generator circuit connected to the microphone to generate a control voltage in response to that portion of the electric energy generated by said one microphone having a predetermined frequency spectrum, a first control circuit connected to the microphone and to the control generator circuit to decrease the lower frequency portions of the electric energy in response to the control voltage from the control generator circuit, and a second control circuit serially connected to the first control circuit and to the control generator circuit to decrease the higher frequency portions of the electric energy in response to the control voltage from the control generator circuit, whereby acoustic energy reconverted from the electric energy has a frequency characteristic suitable for the auditory characteristic of a person having difficulty in hearing.

6. A hearing aid device as claimed in claim 5, wherein the control generator circuit includes rectifier means for rectifying that portion of the electrical energy corresponding to those frequency portions of the acoustic spectrum not required for conversations to generate the control voltage.

7. A hearing aid device as claimed in claim 5, wherein the control generator circuit includes a bandrejection filter for rejecting that frequency portion of the electrical energy corresponding to that frequency portion of the acoustic spectrum required for conversations.

8. A hearing aid device as claimed in claim 5, wherein the control circuit means includes a lowerband control circuit responsive to the control voltage from the control generator circuit to control the lower frequency portions of the electrical energy, and a higher-band control circuit responsive to the control voltage from the control generator circuit to control the higher frequency portions of the electrical energy. 

1. A hearing aid device comprising in combination, a pair of microphones each picking up acoustic energy to convert it to a corresponding electrical energy, a control generator circuit connected to one of the microphones to generate a control voltage in response to that portion of the electric energy generated by said one microphone having a predetermined frequency spectrum, a first control circuit connected to both the other microphone and to the control generator circuit to decrease the lower frequency portions of the electrical energy from the other microphone in response to the control voltage from the control generator circuit, and a second control circuit connected to the first control circuit and also to the control generator circuit to decrease the higher frequency portion of the electrical energy from the other microphone in response to the control voltage from the control generator circuit, whereby acoustic energy reconverted from the electrical energy has a frequency characteristic suitable for the auditory characteristic of a person having difficulty in hearing.
 2. A hearing aid device as claimed in claim 1, wherein the control generator circuit includes rectifier means for rectifying that portion of the electrical energy corresponding to those frequency portions of the acoustic spectrum not required for conversations to generate the control voltage.
 3. A hearing aid device as claimed in claim 1, wherein the control generator circuit includes a band-rejection filter for rejecting that frequency portion of the electrical energy corresponding to that frequency portion of the acoustic spectrum required for conversations.
 4. A hearing aid device as claimed in claim 1, wherein the control circuit means includes a lower-band control circuit responsive to the control voltage from the control generator circuit to control the lower frequency portions of the electrical energy, and a higher-band control circuit responsive to the control voltage from the control generator circuit to control the higher frequency portions of the electrical energy.
 5. A hearing aid device comprising in combination, a single microphone for picking up acoustic energy to convert it to a corresponding electric energy, a control generator circuit connected to the microphone to generate a control voltage in response to that portion of the electric energy generated by said one microphone having a predetermined frequency spectrum, a first control circuit connected to the microphone and to the control generator circuit to decrease the lower frequency portions of the electric energy in response to the control voltage from the control generator circuit, and a second control circuit serially connected to the first control circuit and to the control generator circuit to decrease the higher frequency portions of the electric energy in response to the control voltage from the control generator circuit, whereby acoustic energy reconverted from the electric energy has a frequency characteristic suitable for the auditory characteristic of a person having difficulty in hearing.
 6. A hearing aid device as claimed in claim 5, wherein the control generator circuit includes rectifier means for rectifying that portion of the electrical energy corresponding to those frequency portions of the acoustic spectrum not required for conversations to generate the control voltage.
 7. A hearing aid device as claimed in claim 5, wherein the control generator circuit includes a band-rejection filter for rejecting that frequency portion of the electrical energy corresponding to that frequency portion of the acoustic spectrum required for conversations.
 8. A hearing aid device as claimed in claim 5, wherein the control circuit means includes a lower-band control circuit responsive to the control voltage from the control generator circuit to Control the lower frequency portions of the electrical energy, and a higher-band control circuit responsive to the control voltage from the control generator circuit to control the higher frequency portions of the electrical energy. 